The present invention is directed to a method and apparatus for producing organic acids. More specifically, the present invention is directed to a method and apparatus for producing organic acids from biomass.
Organic acids are important chemicals of commerce. Historically, organic acids were produced from animal fat or vegetable oil sources or from petroleum sources in substantially nonaqueous systems. More recently, organic acids have been identified as among the most attractive products for manufacture from biomass by fermentation. Biomass can be defined as any animal or plant-based material of carbohydrate, protein or fat composition. Among the readily available sources of biomass are municipal solid waste (MSW) and sewage sludge (SS). At present, great expenditures of public funds are used to dispose of such wastes, including costs involved in treatment, transport, incineration or dumping in landfills or oceans of such material. The recovery of valuable products from biomass such as MSW and SS could recover the costs of disposal as well as reduce reliance on nonrenewable fossil fuel resources which serve as feedstock for most industrial organic acid production. Fermentation, therefore, can convert renewable organic materials now considered a costly waste into valuable chemical commodities.
During fermentation, the acids are produced by the microorganisms in dilute aqueous solutions such that recovery of the acids in pure form involves separation from a large quantity of water. Thus, to reduce separation costs, it is desirable to produce the acids at high concentrations. However, at high acid concentrations the fermentation is inhibited which limits the ultimate conversion of the biomass. The acids soon lower the pH of the fermentation medium to a point at which the microorganisms no longer grow or are active. To continue fermentation, the system is purged of acid or the pH is raised by adding neutralizing agents such as ammonia, sodium bicarbonate, calcium hydroxide or calcium carbonate. Addition of neutralizing agents form salts of the acids such as calcium acetate which are substantially less inhibitory than the acids themselves. Nonetheless, these neutralized salts are inhibitory and, at high concentrations, they will also limit the extent of biomass digestion. Accordingly, the need to provide high acid concentration to reduce the cost of product separation is incompatible with the need for maintaining high levels of digestion. Thus there is a need for a method and apparatus for improving the efficiency of producing organic acids from biomass.
Accordingly, a primary objective of the present invention is to provide for a novel and improved method of producing organic acids from biomass by fermentation.
Another objective is to provide for an improved method of producing organic acids by the fermentation of biomass and maintain high biomass digestion and high product concentrations to reduce product recovery costs.
A further objective is to provide for a novel apparatus for converting biomass to organic acids and maintain high biomass digestion rates and high acid concentrations to reduce acid recovery costs.
Still yet an additional objective of the present invention is to provide for an improved reactor for performing fermentation of biomass.
Additional objects, advantages and novel features of the present invention will be set forth in part in the description and claims which follow, and in part will become apparent to those skilled in the art upon examination of the following or can be learned by practicing of the invention.